Displacement map causes strange effects
It looks like you are trying to use bump maps as normal maps.  If your texture data is black and white you should use it as a bump map.  Normal maps are made up of RGB data that maps to the XYZ components of normal vectors.  They generally look purplish blue.  

Plug the output of your noise texture and scratch texture into a mix node, and then plug the output of the mix node into the displacement slot of your material output.



And the result: